OFDM (Orthogonal Frequency Division Multiplexing) is a multi-carrier modulation method with which the transmission data is modulated over multiple sub-carriers and then transmitted in parallel. This method is widely applied in wireless communication systems due to its good characteristics of resisting frequency selective fading and narrow-band interference. The OFDM system is very sensitive to frequency offsets, such as the carrier frequency offset caused by the frequency offset between the transmitter and the receiver. The carrier frequency offset leads to a series of problems, for example, sub-carrier phase rotation, amplitude fading and ICI (inter-carrier interference), which limit the application of the OFDM technology. Therefore, how to cancel the inter-carrier interference is very important for the OFDM system.
A transmission method and apparatus for cancelling inter-carrier interference in OFDM systems is disclosed in a patent application published with No. EP 1496659A1 on Jan. 12, 2005, entitled “Transmitting and receiving apparatus and method in an orthogonal frequency division multiplexing system using an insufficient cyclic prefix”. The OFDM system has N sub-carriers, wherein K sub-carriers are designated as redundant sub-carriers. A transmission apparatus, provided by the patent application, comprises a P filter, for receiving (N-K) data symbols and generating K virtual data symbols, and an IFFT (Inverse Fast Fourier Transformer) having N input taps corresponding to the N sub-carriers. The IFFT receives the (N-K) data symbols and the K virtual data symbols corresponding to the redundant sub-carriers, and performs inverse fast Fourier transformation on the (N-K) data symbols and the K virtual data symbols to output a data frame. Here, the K virtual data symbols are set to a certain value so that the value of the time domain signals that generate ICI is zero in the data frame, resulting in cancellation of the interferences generated among multiple sub-carriers.
In a practical communication system, a plurality of sub-carriers corresponding to an OFDM symbol can generally further carry data with different characteristics, specifically, carry data on the common channels and data on the traffic channels simultaneously. Data with different characteristics will generate different ICI. For example, data on the broadcast channels and the synchronization channels generally will bring larger interference to data transmitted in parallel on the traffic channel due to its higher transmitting power, and sometimes even will become a bottle-neck problem for the transmission design.
There exists a need to provide an effective transmission method and apparatus to cancel interference from a set of consecutive sub-carriers to another set of sub-carriers.